基于分布泵浦结构的高功率掺Tm光纤激光器(英文)

High Power Operation of a Tm-doped Fiber Laser with Distributed Pump Configuration

为了实现掺Tm光纤激光器的高功率连续运转,需要解决半导体激光器输出的低光束质量泵浦光到增益光纤包层的高效耦合问题,以及增益光纤的热管理问题.利用柱面透镜组成的望远镜光学系统对半导体激光器输出泵浦光束进行扩束,使其水平方向的光束发散角获得降低,利用45°反射切割镜对扩束后的光束进行切割,经整形处理后水平方向的光束参量积为84mm·mrad,实现了约70%的光纤端面耦合传输效率.设计了两段增益光纤串联的结构,增加了泵浦光接收端面数,获得了528W的可用泵浦功率.光纤的热管理方面,在泵浦光的输入端部(约250mm),采用了水冷金属热沉散热.基于该实验装置,利用总长度6.4m的掺Tm增益光纤,获得了最高280W的连续输出功率,激光中心波长2 015nm,对应于耦合泵浦功率的斜率效率达55.6%.实验结果表明:通过对半导体泵浦光束的整形处理,可以提高光束对增益光纤的耦合传输效率;双光纤串联的结构在增加可用泵浦功率的同时,降低了光纤端部的热负载,并使整个光纤长度上的热分布更加均匀.

In order to realize the high-power operation of the Tm doped silica fiber laser,there are two issues to be resolved.One is how to couple the pump light with low beam quality into the inner cladding of gain fiber efficiently,the other is on thermal management of gain fiber.For an efficient coupling,firstly the output beam of high power LD modules were collimated to reduce their beam diverge in the plane parallel to the array by use of a telescope system consisting of cylindrical aspheric lenses,and then the collimated beams were cut with splitters.The beam parameter in the plane parallel to the array was optimized to 84 mm · mrad （BPPx）after the reshaping,and a coupling efficiency of 70％ was achieved by this means.A series connection structures consisting of two sections of Tm fiber with identical length were fabricated to increase available pump power and reduce the heat generation along the fiber ends,which achieved a total available pump power up to 580 W.With regard to the thermal management,each end section （250 mm long） of fibers was embedded in a V groove in a water cooled aluminum heat sink.Based on this configuration a continuous-wave output power of up to 280 W operating at 2 015 nm was obtained for 6.4m-long gain fiber,corresponding to a slope efficiency of 55.6％ with respect to the launched pump power.The experimental results indicate that the special reshaping and laser configuration can improve pump coupling efficiency,reduce thermal loading and give more even axial temperature distribution along the gain fibers.